The present invention is related to a dry process for removal of sulfur oxides and nitrogen oxides in a flue gas duct.
The major contributors to acid rain are sulfur oxides, and nitrogen oxides. Sulfur oxides (SO.sub.x) as an air pollutant, include sulfur dioxide (SO.sub.2), sulfur trioxide (SO.sub.3), plus the corresponding acids (H.sub.2 SO.sub.3 and H.sub.2 SO.sub.4) and salts (sulfites and sulfates). Nitrogen oxides (NO.sub.x), in air pollution terminology refer to two gaseous oxides of nitrogen, nitrogen dioxide (NO.sub.2) and nitric oxide (NO). The predominant species in flue gas are SO.sub.2 and NO. SO.sub.x can generally be controlled reasonably well by flue gas desulfurization processes. Dry Flue Gas Desulfurization (DFGD), also called Spray Dry Flue Gas Desulfurization (SDFGD), is a sulfur dioxide scrubbing process in which lime slurries, or alternatively, sorbent solutions containing sodium compounds such as sodium bicarbonate, are contacted with flue gas in a device such as a spray dryer, in which the sulfur dioxide reacts with the sorbent material, and the water simultaneously evaporates. The resulting product is a dry mixture of CaS.sub.3, CaSO.sub.4 unreacted sorbent, and flyash. A baghouse located downstream from the spray absorber removes entrained particulates.
It is expected that acid rain regulations will require the scrubbing of nitrogen oxides (NO.sub.x), as well as sulfur oxides (SO.sub.x). Proposed targets for stack gas cleanup are 90% SO.sub.x /90% NO.sub.x and 50% SO.sub.x /50% NO.sub.x for new and retrofit applications, respectively. One of the major issues which inhibits the implementation of retrofit scrubbers by electric utilities in the high cost of the scrubbers and, thus, the resultant increased cost of electricity. Although chemistries to remove SO.sub.x are well known and have been successfully implemented for a number of years, NO.sub.x removal chemistries compatible with these SO.sub.x removal systems are not effective.
It is an object of the present invention to provide a low cost process for the removal of both SO.sub.x and NO.sub.x which eliminates the need for a spray dryer.